Laboratory leaching tests on treated wood according to different harmonised test procedures

Abstract

Background: Laboratory leaching tests on treated wood were performed during a European robustness study in the framework of the validation of a tank leaching test procedure that has been proposed for construction products in order to determine the potential release of dangerous substances which can be transferred to soil and groundwater. The release of substances has to be determined also for materials treated with biocidal products according to the requirements of the European Biocidal Products Regulation. A similar leaching test procedure was already harmonised for treated wood for this purpose. Both test procedures were applied in parallel to wood treated with the same preservative to investigate whether the results of these tests can replace each other. Additional experiments were performed to further investigate unexpected effects of L/A ratio on leaching of copper and duration of storage of treated test specimens. Results: Both procedures generate similar results concerning cumulative emissions of tebuconazole, copper, dissolved organic carbon and total nitrogen. The emission rates with time are in comparable ranges for both leaching protocols. Emissions of copper increased with decreasing L/A ratios. Strong correlation of copper concentrations and dissolved organic carbon as well as total nitrogen concentrations in eluates indicates that this observation is caused by co-elution of copper with organic substances. Duration of storage of treated test specimens affected emissions for the investigated wood preservative. Conclusions: Based on these findings, results from both test procedures can be used to describe leaching characteristics and avoid double testing of treated wood to fulfil the requirements of the European regulations for either biocides or construction products. Leaching of substances from treated wood is a complex process that depends on its chemical composition and ageing processes.

The extent of tebuconazole leaching from unpainted and painted softwood

“…1 While the leaching behavior of inorganic preservatives has been extensively studied, [2][3][4] leaching of organic preservatives has been investigated to a lesser extent, and was limited to pressure-treated wood using mainly metal-containing formulations. [5][6][7][8][9][10] Triazoles such as tebuconazole (TAZ) and propiconazole are among the most frequently used organic wood preservatives, [11][12][13][14][15] thus determination of their leaching potential under various conditions is warranted.…”

“…19 In addition to using metals as part of the formulation, the majority of studies were performed on pressure-treated wood that was fully immersed into water. 6,[9][10]16 Pressure treatment of wood (e.g., wood impregnation with preservatives under pressure) is commonly used for ground contact wood (e.g., decks) to increase the penetration depth and active loading. 23 However, in North America, nearly all of the wood used to produce windows and door frames is dip treated, 13 which is cost-effective and ensures sufficient concentration of preservatives near the wood surface.…”